1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor device using an organic substrate formed by an organic material such as a resin material.
The organic substrate is used for substrates of semiconductor devices due to its easiness in handling and processing. As a typical organic substrate, there is a glass-epoxy substrate or a polyimide substrate. In a semiconductor device using the organic substrate, it is general to fix a semiconductor chip to the organic substrate by an adhesive.
However, the organic substrate has a high moisture-absorption characteristic, thereby having a nature to easily absorb moisture in an atmosphere. An amount of moisture absorbed by the organic substrate can be reduced if the semiconductor device is stored in a low humidity atmosphere. However, there may be a problem related to a static electricity if the humidity is low. Thus, it is required to maintain the humidity at a certain level.
Accordingly, the organic substrate is used on the assumption that the organic substrate absorbs a certain amount of moisture, and a semiconductor device using an organic substrate is generally provided with means for preventing problems caused by moisture absorbed by the organic substrate.
2. Description of the Related Art
The moisture absorbed by an organic substrate in a semiconductor device remains at an interface between the organic material and an adhesive or under fill material that fixes a semiconductor chip onto the organic substrate. When such moisture is heated due to a heat for mounting the semiconductor device, the moisture is abruptly evaporated, which increases an inner pressure. Thus, there is a problem in that the adhesive is separated from the organic substrate at the interface therebetween. Such a separation is referred to as a popcorn phenomenon.
As measures for preventing the popcorn phenomenon, a method is used in which a plurality of small though holes generally referred to as vent holes are formed in the organic substrate so as to release a water vapor, which is generated at the interface between the adhesive and the organic substrate, via the through holes.
FIG. 1 is a cross-sectional view of a conventional semiconductor device produced by a wire bonding method. A semiconductor chip 2 is fixed to an organic substrate 6 via an adhesive 4. Electrodes of the semiconductor chip 2 are connected by bonding wires 8 to electrode pads 10 formed on the organic substrate 6, respectively. The semiconductor chip 2 and the bonding wires 8 are encapsulated by a seal resin 12. Additionally, the electrode pads 10 of the organic substrate 6 are electrically connected to solder balls 14, which are external connection electrodes, via a circuit pattern (not shown in the figure) formed on the organic substrate 6.
In the semiconductor device shown in FIG. 1, a plurality of vent holes 16, which are through holes, are previously formed in the organic substrate 6 so as to prevent the above-mentioned popcorn phenomenon. Since the vent holes 16 are formed by punching or drilling, a diameter of each of the vent holes 16 ranges from 0.1 mm to 0.3 mm. The semiconductor device is formed by fixing the semiconductor chip 2 by the adhesive 4 onto the organic substrate 6 having the thus-formed vent holes 16.
Additionally, there is a method in which the vent holes 16 are not previously formed on the organic substrate 6 but a plurality of through holes are formed as the vent holes 16 in the organic substrate 16 by using a laser apparatus 18 after fixing the semiconductor chip 2 to the organic substrate 6 and encapsulating by a resin.
FIG. 3 is a cross-sectional view of a conventional semiconductor device produced by a flip chip method. The semiconductor chip 2 is mounted to the organic substrate 6 by bonding stud electrodes 20 to the electrode pads 10 formed on the organic substrate 6. An under fill material 22 is filed between the semiconductor chip 2 and the organic substrate 6 so as to securely fix the semiconductor chip 2 to the organic substrate 6. Additionally, the electrode pads 10 of the organic substrate 6 is electrically connected to the solder balls 14, which are external connection electrodes, via the circuit pattern (not shown in the figure) formed on the organic substrate 6. The under fill material 22 corresponds to the adhesive 4 in FIG. 1.
Accordingly, similar to the semiconductor device shown in FIG. 1, the vent holes, which are a plurality of through holes, are previously formed in the organic substrate 6. Since the vent holes 16 are formed by punching or drilling, a diameter of each of the vent holes 16 ranges from 0.1 mm to 0.3 mm. The semiconductor device is formed by fixing the semiconductor chip 2 onto the organic substrate 6 having the thus-formed vent holes 16 and filling the under fill material 22 between the organic material 6 and the semiconductor chip 2.
Additionally, there is a method in which the vent holes 16 are not previously formed on the organic substrate 6 but a plurality of through holes are formed as the vent holes 16 in the organic substrate 16 by using the laser apparatus 18 after fixing the semiconductor chip 2 onto the organic substrate 6.
In the semiconductor device shown in FIG. 1, since the vent holes 16 are previously formed in the organic substrate 6, there is a problem in that the adhesive 4 leaks through the vent holes 16 when the liquid or paste-like adhesive 4 before curing is supplied between the semiconductor chip 2 and the organic substrate 6.
The adhesive 4 is mixed with filler having a particle diameter ranging from 50 xcexcm to 60 xcexcm, and, thus, the filler easily passes through the vent holes 16, and the vent holes 16 are not clogged by the filler. However, the leakage of the adhesive 4 cannot be prevented by the filler.
If the adhesive 4 leaks through the vent holes 16, the leaking adhesive may cause a problem during a mounting operation of the semiconductor device. That is, the leaked and cured adhesive 4 may adhere to the electrodes of the mounting substrate when the semiconductor device is mounted onto the mounting substrate, which may cause incomplete soldering.
In order to eliminate the above-mentioned problem caused by the leakage of the adhesive 4, the vent holes 16 are formed by laser machining after the adhesive 4 is cured as shown in FIG. 2. Thereby, the leakage of the adhesive 4 can be prevented, but there is a problem in that a surface of the semiconductor chip 2 is damaged by a laser beam penetrating the adhesive 4 and reaching the surface of the semiconductor chip 2. In recent years, semiconductor chips have become thin, and, therefore, a crack may be generated in the semiconductor chip 2 when the semiconductor chip receives only a small damage. When the semiconductor chip 2 receives damage, an operation failure may occur in the semiconductor device.
Additionally, in the semiconductor device shown in FIG. 3, there is the same problem as the above-mentioned semiconductor device shown in FIG. 3. That is, in a case in which the vent holes 16 are previously formed in the organic substrate 6, there is a problem in that the under fill material 22 leaks through the vent holes 16. Additionally, as shown in FIG. 4, in a case in which the vent holes 16 are formed in the organic substrate 6 by laser machining after the under fill material is cured, the surface of the semiconductor chip 2 may be damaged by the laser beam.
Especially, in the semiconductor chip produced by the flip chip mounting as shown in FIGS. 3 and 4, since the circuit forming surface of the semiconductor chip 2 faces the organic substrate 6, the circuit forming surface is damaged by the laser machining. Accordingly, the circuit of the semiconductor chip is directly influenced even if the damage is very small, which results in an operation failure of the semiconductor device.
It is a general object of the present invention to provide a semiconductor device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a semiconductor device having vent holes through which an adhesive or under fill material does not leak.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor device comprising:
a semiconductor element;
a substrate having a first surface on which the semiconductor element is fixed and a second surface opposite to the first surface;
an adhesive provided between the semiconductor element and the first surface of the substrate;
at least one though hole extending between the first surface and the second surface of the substrate; and
a pattern member formed on the first surface of the substrate so as to cover a part of an opening of the through hole.
According to the present invention, since the pattern member formed on the first surface of the substrate partially covers the opening of the through hole of the substrate, the diameter of the through hole is substantially reduced. Accordingly, the presence of the pattern member prevents the adhesive from leaking though the though hole even if the actual size of the through hole is such that the adhesive easily passes though the through hole. The pattern member partially covers the through hole, and, thereby, a part of the though hole is open to the adhesive retained on the first surface of the substrate. Accordingly, the water vapor generated at an interface between the first surface of the substrate and the adhesive can be discharged through the through hole.
In the semiconductor device according to the present invention, the pattern member may be formed of the same material as electrode pads formed on the first surface of the substrate. Accordingly, there is no need to provide a separate process so as to form the pattern member. Thus, the semiconductor device according to the present invention can be achieved without increasing a manufacturing cost.
Additionally, the pattern member may be a circuit pattern formed on the first surface of the substrate so that there is no need to provide the pattern member only for partially closing the through hole. That is, the circuit pattern partially covers the through hole, and, thereby, the diameter of the through hole is substantially reduced. Accordingly, the presence of the circuit pattern prevents the adhesive from leaking though the though hole even if the actual size of the through hole is such that the adhesive easily passes though the through hole. Additionally, there is no need to provide the though hole at a position which avoids the circuit pattern as in the conventional device, thereby improving a freedom of design of the substrate.
Additionally, in the semiconductor device according to the present invention, the substrate may be an organic substrate formed of an organic material. The organic substrate is inexpensive and can be easily handled. However, the organic substrate has a drawback in that it has a high moisture-absorbing characteristic. The moisture absorbed by the substrate stays between the adhesive and the substrate, and causes a problem in that the adhesive is separated from the substrate by an abrupt evaporation due to heating for mounting the semiconductor device. Accordingly, by forming the pattern member on the organic substrate so as to partially cover the though hole for discharging the water vapor, the semiconductor device can be manufactured at a low cost without increasing the manufacturing cost while compensating for the drawback of the organic substrate.
Additionally, there is provided according to another aspect of the present invention a manufacturing method of a semiconductor device, comprising the steps of:
forming a pattern member by a metal on a first surface of a substrate;
fixing a semiconductor element onto the first surface of the substrate; and
irradiate a laser beam onto a position at which the pattern member is formed from a side of a second surface opposite to the first surface of the substrate so as to form a vent hole that penetrates the substrate.
According to the above-mentioned manufacturing method, the adhesive does not leak from the through hole since the though hole is formed by laser machining after the adhesive has been cured. Additionally, since a metal-made pattern member, which reflects a laser beam, is formed on a portion of the substrate facing the adhesive at which the laser machining is applied, the semiconductor element is prevented from being damaged by the laser beam even if an excess laser beam is irradiated onto the semiconductor element after the formation of the though hole is completed. Thus, the though hole can be formed while the semiconductor is prevented from being damaged without increasing an accuracy of control of the laser beam power.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.